For many years tars and pitches have been used to fill the joints and cracks between adjacent concrete slabs which are used as highway and airfield pavements and to form films or waterproofing membranes on concrete slabs or on roofs. Tars and pitches in their native form have many unsatisfactory characteristics for these purposes. For example, tars and pitches in their native form get very brittle in cold weather and tend to crack and lose the bond between the tar or pitch and the concrete slab. As a result, water penetrates the joint and freezing and thawing cycles cause the slabs to break up. In very warm weather, tars and pitches becomes soft and tacky, which in turn causes them to be extruded from the sides of a crack when exposed to vertical forces caused by traffic. In addition, tacky tars and pitches tend to stick to vehicle wheels causing a problem known as tracking, in which the tar or pitch is removed from the crack by adhering to a vehicle wheel and it is subsequently spread over the surface of the pavement by contact between the wheel and the pavement.
Native tars and pitches are particularly vulnerable when used in airfield pavements because they are soluable in jet fuel and because they liquify in the heat of a jet engine blast.
Many of the above mentioned problems have been solved by the advent of blends of coal tar pitch and vinyl chloride polymers, hereinafter PVC. Blends of coal tar pitch and PVC form rubber-like gels that remain flexible in cold weather and rubber-like in hot weather. The PVC-coal tar pitch mixture exhibits good adhesion to concrete and good cohesion so that the joint between adjacent slabs remains sealed against moisture penetration. Although the PVC-coal tar pitches known to the art are excellent sealants for cracks between concrete slabs, they do not adhere well to asphaltic pavements. Thus, for example, a joint between a concrete pavement slab and an asphaltic shoulder cannot be sealed with these otherwise excellent joint sealants because thermal expansion and contraction will cause a separation between the joint sealant and the asphaltic slab so that moisture can penetrate and damage the pavement.
PVC-coal tar mixtures made in accordance with U.S. Pat. No. 3,549,575 and its reissue U.S. Pat. No. Re. 29,548 are particularly desirable joint sealants because they are liquid phase at room temperatures and therefore can be easily heated to application temperature and introduced into a joint or crack in a highly fluid condition which causes excellent penetration and avoids the formation of bubbles or blisters within the joint. Joint sealants frequently are made more fluid by incorporating fluidizers or plasticizers within their composition. Typical of these are octylpthalates which are very expensive and, although used in small proportions, constitute a significant portion of the total cost of a joint sealant composition.
Joint sealants commonly have critical composition limitations and require blending of their ingredients to be done expertly. Accordingly, it is desirable that joint sealants be completely made in the factory so that no blending or compositing need be done in the field. It is desirable that joint sealants be in a liquid state in their shipping containers and that the joint sealants in their containers have long shelf life so that the material is liquid at the time of use. Joint sealants commonly are heated in a melter/applicator at the site where they are applied in the joints to cause certain physical and chemical reactions to take place that puts the sealants in a condition where they set up in the joint to the desirable adhesive, cohesive, rubbery form. It is desirable that joint sealants have a long pot life, specifically that they have the ability to be maintained hot in the melter where they are heated at the site of application for a relatively long period before the setting-up reactions occur. As stated above, it is very desirable for the joint sealant to be highly fluid when it is applied and it is accordingly necessary to heat the joint sealant material to a temperature that is high enough to give it the proper degree of fluidity. Ordinarily, higher temperatures accelerate the setting up reactions and accordingly very viscous joint sealant materials must be heated to a higher temperature in the melter at the site of application and have a correspondingly shorter pot life.
Joint sealants that are useful for filling joints between asphalt and concrete or for filling cracks in asphalt pavement are known. U.S. Pat. Nos. 3,844,668 and 3,919,148 describe such joint sealants. These materials are made of paving asphalt, ground rubber, and a solvent. These materials suffer from being very viscous and having a significant proportion of their total composition in the form of a solvent. The solvent evaporates from the mixture leaving the mixture less dense, the solvent creates a fire hazard in the heating of the mixture, and the solvent creates a pollution problem when it evaporates from the hot composition as it is applied and after it is in place. In addition, the prior art compositions that are useful for sealing joints in asphalt contain a high proportion of rubber which is expensive and which inherently increases the viscosity of the mixture at any given temperature.